Lithium-ion secondary batteries have positive and negative electrodes that can reversibly absorb and desorb lithium ions, and an electrolyte interposed between the both electrodes, and perform perform charge and discharge by moving back and forth of lithium ions between the both electrodes. Lithium-ion secondary batteries are used as a power source in various kinds of portable devices because they are lightweight and have a high energy density. Moreover, the use of lithium-ion secondary batteries has been studied in fields that require large capacity power sources such as hybrid automobiles, electric automobiles, and the like where even greater improvement in battery performance is needed. More specifically, excellent high-temperature storage characteristics are important in lithium-ion secondary batteries intended for application in automobiles and other environments in which usage and storage temperatures can become high.
Patent Document 1: Japanese Patent Application Laid-open No. 2001-6729
Patent Document 2: Japanese Patent Application Laid-open No. 2002-352852